1. Field of the Invention
The present invention relates, in general, to scanning apparatuses using a plurality of diffracted beams and, more particularly, to a scanning apparatus, which can scan a plurality of diffracted beams formed by diffracting and modulating light generated by a single light source onto a scanning object, such as the drum of a printer and a sheet.
2. Description of the Related Art
Light beam scanning apparatuses are devices for scanning light beams and forming the spots of the light beams on a photosensitive medium to form an image in an image formation device, for example, a laser printer, a display device, a Light Emitting Diode (LED) printer, an electronic photocopier or a word processor.
As image formation devices have been developed toward the requirements of miniaturization, high speed and high resolution, such a light beam scanning apparatus has been gradually researched and developed to obtain the characteristics of miniaturization, high speed and high resolution so as to meet the requirements.
The light beam scanning apparatuses of an image formation device can be classified into a laser scanning scheme using an f·θ lens and an image head printing scheme according to a light beam scanning scheme and the construction thereof.
FIG. 1 is a view showing a conventional laser scanning apparatus using an f·θ lens.
As shown in FIG. 1, the conventional laser scanning apparatus includes a Laser Diode (LD) 100 for emitting a light beam in response to a video signal, a collimator lens 101 for converting the light beam emitted from the LD 100 into collimated light, a cylindrical lens 102 for converting the collimated light output from the collimator lens 101 into linear light parallel to a scanning direction, a polygon mirror 103 for moving and scanning the parallel linear light from the cylindrical lens 102 at a constant linear velocity, a polygon mirror driving motor 104 for rotating the polygon mirror 103 at a uniform velocity, an f·θ lens having a certain refractive index relative to an optical axis to deflect light, reflected from the polygon mirror 103 and moved at a constant angular velocity, in a main scanning direction, correct aberration and focus the light onto a scanning surface, a reflective mirror 106 for image formation for reflecting laser beams output from the f·θ lens 105 in a predetermined direction and forming an image using the reflected laser beams on the surface of a photosensitive drum 107, which is an image formation surface, in the form of spots, a horizontal synchronizing mirror 108 for reflecting the laser beams from the f·θ lens 105 in a horizontal direction, and an optical sensor 109 for receiving laser beams reflected from the horizontal synchronizing mirror 108 and synchronizing the laser beams.
In the conventional laser scanning apparatus having the above construction, the light beam output from the LD 100 is converted into collimated light by the collimator lens 101, focused in the direction of the rotation shaft of the polygon mirror 103 by the cylindrical lens 102, and reflected by the polygon mirror 103 rotating at a constant angular velocity. Light beams, reflected by the polygon mirror 103, pass through the f·θ lens 105, and the passed light beams are formed as spots, each with a certain diameter, on the photosensitive drum 107. In this case, since the resolution of a printer is determined with the diameter of the spots formed on the photosensitive drum 107, the machinability of the f·θ lens must be excellent.
However, a light beam scanning apparatus must be generally considered from the aspect of miniaturization and cost. Therefore, in order to reduce the number of lenses in the f·θ lens, the f·θ lens includes a Y-toric surface, an anamorphic surface, a freeform surface, etc. Therefore, since it is difficult to form the surface of the f·θ lens, the machinability thereof is deteriorated. Consequently, there is a disadvantage in that the performance and resolution of the light beam scanning apparatus are deteriorated.
Further, the above-described conventional scanning apparatus is problematic in that, since printing speed is proportional to the rotation speed of a polygon mirror, and one line is printed with respect to each side of the polygon mirror, the rotation speed of the polygon mirror must be further increased in the case where high speed printing is performed, so that a time for which a laser beam is radiated is reduced, and a laser diode having high power must be used to obtain the same light scanning effect.
If the conventional scanning apparatus having the above problem is used in a printer, there are problems in that, since an expensive high speed polygon mirror must be used, the cost is greatly increased, and printing speed cannot be increased to a certain level or higher.